pH-meters are milivoltmeters of direct current with high input resistance, calibrated in pH or pH and mV units. 

pH-meter calibration consists in testing the instrument operation correctness, including the determination of the relation between reference standard and tested instrument indications, in order to check the indication error and uncertainty in the measurement range of the calibrated pH-meter.

pH-metering electrode calibration is performed in order to determine the characteristic slope, efficiency and zero point value of the electrode, as well as the uncertainty of those parameters.

redox electrodes

Calibration of the redox electrode is carried out in order to determine the potential error of the oxidation-reducing electrode with uncertainty.